1. Field of the Invention
The present invention relates to a control apparatus for a vehicular automatic transmission, and more particularly to a control apparatus for an automatic transmission which inhibits switching between ranges when a shift lever is erroneously operated.
2. Description of the Prior Art
When a shift lever is erroneously switched to a reverse range in forward driving of a vehicle, and when the shift lever is switched to a forward range in reverse driving, hard braking occurs to cause engine stop. To prevent this, it is necessary to inhibit accomplishment of gear shift to the selected range without engaging friction elements that should be engaged in response to the switching operation.
To this end, it is disclosed in Japanese Laid-Open Patent Publication No. H06-272757 that control is provided such that when a shift lever is switched from a forward range to a reverse range in driving of a vehicle at a predetermined vehicle speed or higher, gear shift to a reverse gear position is inhibited from being accomplished, and when the shift lever is switched from the reverse range to the forward range, the gear position is temporarily changed to the third speed gear position.
As another example, it is disclosed in Japanese Laid-Open Patent Publication No. H05-126248 that control is provided such that when a shift lever is switched from one range to another, the range that has been continuously set for a predetermined period of time and the newly selected range are compared with each other, and when they are different, gear shift to the newly selected range is inhibited from being accomplished.
According to Japanese Laid-Open Patent Publication No. H06-272757, when the range is switched to the forward range in response to an erroneous operation of a shift lever, the gear position is temporarily changed to the third speed gear position. However, even when a driver notices the erroneous operation and returns the shift lever to the normal position (reverse range), accomplishment of gear shift to a reverse gear position is inhibited by inhibition control, and hence the gear position is kept at the forward third speed gear position irrespective of the driver's operation, and therefore the vehicle cannot run rearward.
Also, in the case where the shift lever is erroneously switched to the reverse range while the vehicle is running forward, when the driver notices the erroneous operation and returns the shift lever from the reverse range to the normal position (forward range) with gear shift to a reverse gear position being not accomplished, this operation is also determined as being an erroneous operation, and the gear position is switched to the forward third speed gear position, thereby causing driving force to be considerably changed as compared with the original driving force.
On the other hand, according to Japanese Laid-Open Patent Publication No. H05-126248, whether switching between ranges is to be accomplished or not is determined based on a range that has been continuously set for a predetermined period of time, but for example, when switching between the forward range and the reverse range by the shift lever as in the case where a vehicle is turned in a K-turn in a parking lot is a normal operation suited to the driver's intension, gear shift to a gear position of the range selected by the shift lever needs to be accomplished as fast as possible from the standpoint of responsiveness, and therefore it is preferred that the above-mentioned predetermined period of time is short. If, however, the predetermined period of time is set to be short, there is a problem that in the case where the shift lever is erroneously operated while the vehicle is running at a high speed, the range is switched to the range selected by the erroneous operation before the vehicle speed becomes low, and hence the occurrence of engine stop cannot be prevented.